Acetic acid, one of the more important aliphatic intermediates, quantitatively ranks among the commodity chemicals produced in large tonnage quantities. However, availability of acetic acid for downstream applications can be limited at times since availability and price of feedstocks for the production of acetic acid are subject to constant change. For example, availability of hydrocarbon feedstocks such as ethylene, butane and butenes from petroleum and natural gas sources can vary widely depending upon supplies of crude oil upon the world market, capacity of petrochemical producers and demand for products which utilize these same hydrocarbons as feedstocks. An example is polyethylene from ethylene.
Acetic acid can be manufactured by one of several processes, i.e., from acetaldehyde or alkanes and alkenes by oxidation, by carbonylation of methanol, among others. Some of these other processes include the oxidizing of methylcyclohexane to produce acetic acid and formic acid, U.S. Pat. No. 3,247,249; vapor phase oxidation of ethyl alcohol in the presence of a solid palladium metal containing catalyst, U.S. Pat. No. 3,739,020; liquid phase oxidation of ethyl alcohol in the presence of at least one ketone such as methylethyl ketone and at least one aldehyde such as acetaldehyde and using air, cobalt acetate catalyst and acetic acid reaction medium, U.S. Pat. No. 3,914,296.
It is well-known that carboxylic acids such as acetic acid can be produced by several other liquid phase processes including the liquid phase oxidation of various organic compounds, such as ethanol to acetic acid. For example, in U.S. Pat. No. 2,425,878, a liquid phase oxidation process involves the direct reaction of a lower aliphatic alcohol, ethanol, with oxygen in a liquid phase reaction to prepare acetic acid wherein a rare earth metal catalyst is activated by an aldehyde. Large amounts of catalyst and activator are required.
In the past, high rates of conversion have been obtained in the utilization of ethanol to prepare acetic acid by use of an activator or promoter, as for example, when an aldehyde such as acetaldehyde is used as an activator, as in U.S. Pat. No. 2,578,306.
Although excellent yields of acetic acid are obtained, large amounts of promoter are required, from 1.6 to 9 moles acetaldehyde/mole ethanol oxidized (see U.S. Pat. No. 2,578,306), and from 0.41 to 1.26 moles, acetaldehyde plus methyl ethyl ketone/mole ethanol, oxidized (see U.S. Pat. No. 3,914,296). The problem with using such large amounts of acetaldehyde and methylethyl ketone to prepare acetic acid from ethanol is while these compounds oxidize to form acetic acid themselves, these compounds cost more than ethanol or acetic acid and are not commercially available in large enough amounts to make a large scale ethanol-to-acetic acid process practical. The instant invented process uses a cobalt, manganese, and bromine catalyst system and does not require additional promoters.
Oxidation of ethanol to acetic acid using a cobalt, manganese, bromide catalyst is taught in U.S. Pat. No. 3,247,249, "Preparation of Formic and Acetic Acids by Oxidizing Methylcyclohexane or Paraffin Wax in the Presence of Manganese Bromide." The yield of acetic acid and selectivity to acetic acid are far lower using the reaction conditions described in U.S. Pat. No. 3,247,249 than yields obtained by other processes, including yields obtained by processes using an activator or promoter. Yields of acetic acid given in the examples range from 12 to 19 mole % with formic acid being the major product in 61 to 64 mole % yield.
The bromine-polyvalent-metal catalysis system in acetic acid solvent has been in commercial use in many countries for the manufacture of terephthalic acid from p-xylene for many years. In the absence of acetic acid solvent, yield of a single phthalic acid (e.g., terephthalic acid) on a once through basis of the xylene, amounted to about 20 weight percent (12.8 mole), according to U.S. Pat. No. 2,833,816. Since terephthalic acid, for example, is the starting material for polyethylene terephthalic (PET) which is the principal polymer for polyester fibers, polyester films, and resins for bottles and like containers, the importance of acetic acid in the preparation of terephthalic acid, and in the preparation of other aromatic polycarboxylic acids, cannot be doubted.
In the oxidation of polyalkyl aromatics to polycarboxylic acids in the presence of acetic acid, as a solvent, some acetic acid is oxidized to carbon oxides and other oxidation by-products, which, coupled with physical losses, requires a constant addition as make-up to the oxidation process. Large quantities of acetic acid accordingly are required to supply the required amount of acetic acid necessary for production of, as an example, terephthalic acid on a commercial scale.
However, despite the availability of acetic acid from many sources, the singular importance of acetic acid as a solvent in production of polycarboxylic acids from alkyl aromatics, and the possibility of an interruption in the supply of acetic acid from conventional processes, mandated a search for a process to generate acetic acid in situ with the oxidation of polyalkyl aromatics to polycarboxylic aromatic acids.
It has been discovered that utilization of a cobalt-manganese-bromine-containing catalyst without added promoters in the preparation of terephthalic acid from p-xylene, isophthalic acid from m-xylene, and the preparation of trimellitic acid from pseudocumene makes possible the production of acetic acid from ethanol in high conversion, good selectivity and yield wherein the resulting acetic acid is the solvent of choice for oxidation of p-xylene to terephthalic acid, or oxidation of m-xylene to isophthalic acid, or oxidation of pseudocumene to trimellitic acid. In the process of this invention, formic acid is not produced as the major product, in contrast to the process of U.S. Pat. No. 3,247,249, wherein formic acid is the major product in 61 to 64 mole % yield and yields of acetic acid range from 12 to 19 mole %.
It is an object of the instant invention to provide a process for the production of acetic acid as a co-product in the oxidation of polyalkyl aromatics to polycarboxylic aromatic acids.
It is an object of the instant invention to provide a catalytic process for production of acetic acid as a co-product in the oxidation of polyalkyl aromatics to polycarboxylic acids wherein the catalyst comprises a variable valence oxidation catalyst in the presence of a bromine ion, preferably a cobalt-manganese catalyst in the presence of bromine ion.
It is an object of the instant invention to provide a catalytic process for production of acetic acid as a co-product in the oxidation of polyalkyl aromatics to polycarboxylic acids wherein the catalyst comprises cobalt-manganese-bromine, ethyl alcohol is oxidized to acetic acid, and production of formic acid, as a co-product from oxidation of ethyl alcohol, is minimized.
It is an object of the instant invention to provide a catalytic process for production of a C.sub.2 -C.sub.6 aliphatic monocarboxylic acid as a co-product in the oxidation of polyalkyl aromatics to polycarboxylic acids and wherein the catalyst comprises cobalt-manganese-bromine, wherein a C.sub.2 -C.sub.6 lower aliphatic alkanol is oxidized to a corresponding C.sub.2 -C.sub.6 aliphatic monocarboxylic acid.